INTUODUCTOKT. 11 



la composition. When dried at 100° Cent., milk-sugar 

 has the formula as given above, viz., CijH^jOuHjO; cane- 

 sugar, on the contrary, when dried at 100° Cent., exhibits 

 the composition CizHjjOn. Heated to about 140" Cent., 

 milk-sugar loses an atom of water, and becomes CuHjjOi,. 



In solubility in water there is much difference between the 

 two. Milk-sugar dissolves in five or six parts of cold water 

 and in two and a half parts of boiling water. Cane sugar, 

 on the other hand, is far more soluble. It dissolves in one 

 third of its volume of cold water, and in exceedingly little 

 boiling water. 



Milk-sugar is not so heavy as cane-sugar, its specific 

 gravity being 1.53 ; whilst cane-sugar has a specific gravity 

 of 1.606. 



Towards alkaline-copper-solution, the behavior of the 

 two kinds of sugar is quite different ; whereas milk-sugar 

 reduces the oxide to the suboxide of copper even in the cold, 

 solution of cane-sugar does not even effect a reduction, on 

 being heated to the boiling point of water. 



The Ash, or Mineral Matter. — When milk is dried up, and 

 the dried residue afterwards incinerated, the ash remains 

 behind. This consists mainly of phosphate of iime, which 

 forms about two-thirds of it, and of chlorides. There is 

 hardly any free or carbonated alkali in the ash of cow's 

 milk. The degree of freedom of the ash from alkali may 

 be judged of from the fact, ascertained by myself, that the 

 ash does not neutralize as much standard acid as it would if 

 one hundredth of its weight consisted of alkaline-carbonate. 



Such, then, are the component parts of milk. It remains 

 to be added, that milk has a specific gravity of about 1.029, 

 at 15.6 C, and that its physical appearance is very peculiar. 

 It is not a clear liquid, being, in point of fact, an emulsion. 

 Left to itself, it by and by becomes surmounted with a 

 whitish layer, well known as cream . When fresh, it is very 



